Common sense if the whole rock is natural then those cracks would extend naturally up to the other side of the rock. Look the half part was just molded and stuck to a natural rock at the left part. They were expert in producing natural looking rocks and soil back fill.
This is what i am telling to lot of hunters "you must outwit the cleverness of Japanese sign and marker making ingenuity in order to succeed" it is a starting point for your success...